1. Field of the Invention
The present invention relates to charge transfer semiconductor devices and, more particularly, to a charge coupled semiconductor device (CCD).
2. Description of the Prior Art
Unlike prior-art semiconductor devices of the construction in which P-N junctions are formed within a semiconductor, the charge coupled semiconductor device uses as an information transmitting medium, charges existing in the vicinity of the surface of a semiconductor substrate, and controls the transfer of the charges by a voltage applied to a gate electrode. It has various features such as a small number of manufacturing steps and a good yield, and recently has acquired considerable attention in the art.
The semiconductor device, however, merely employs the charges present in the vicinity of the surface of the substrate as the information transmitting medium, and successively transfers them. It effects substantially no amplifying operation. Furthermore, the charges (carriers) being transferred move along the surface of the substrate, so that they are sometimes trapped halfway between the transfer electrodes to lower the transfer efficiency. It has hitherto been of importance to imcrease the transfer efficiency. A variety of proposals have, therefore, been made, any of which, however, provides an improvement merely by changing the working bias conditions, not by modifying the construction of the device itself. Although the characteristic under the gate electrodes can be improved to some extent, no attention has been paid to the trap phenomenon in the area between the gate electrodes which cannot be externally and directly controlled by the bias.